This is a story about journalists and a threat to press freedom. It is also a story about journalistic courage and, perversely, one about journalistic failure. Before we get there, however, it is necessary to provide a giant slab of context.

We are in Northern Ireland, where farce and tragedy have so often been intertwined, and this latest manifestation centres on the aftermath of six murders committed in 1994. Here is the tragedy. On a June evening, men were gathered in a small bar in a County Down village to watch Ireland play Italy in a World Cup match when two men wearing boiler suits and balaclavas burst through the door.

One shouted “Fenian bastards” and opened fire at point blank range with an assault rifle. After spraying the TV watchers with 60 rounds, the gunmen walked out and calmly got into a car. They left behind six dead men and five more suffering from bullet wounds. It has been known ever since as the “Loughinisland massacre”.

This appalling story may be one, with the passing of time, you have forgotten, or possibly one you never knew about. Within Britain, it did not receive anything like the news coverage it merited, partly because of the attention paid to the opening stages of the peace process and partly because there were no developments deemed to be newsworthy.

Now comes the opening act of the farce. Although the community of Loughinisland, and a swathe of people across Northern Ireland, quickly knew that the loyalist paramilitary group, the UVF, was responsible, and could even name suspects, no one was charged.

There was abundant evidence available to the police, the now-disbanded RUC, such as the abandoned getaway car, the gunmen’s discarded clothing and the rifle. It should have been a forensic triumph, but no genuine attempt was made to use it. Suspects were eventually questioned but their brief arrests were no more than a cynical publicity stunt.

Observers wondered whether the police inaction might be due to at least one of the killers being an RUC informant who was being shielded from prosecution. Amid the whispers of collusion, the bereaved relatives of the six men waited patiently for action. When none came they began, tentatively at first, but with growing commitment, to campaign for justice. All we want, they kept saying, was the truth.

They were often thwarted, not least by the 2011 investigation by the Northern Ireland police ombudsman, which produced an alphabet soup – Person A, Police Officer 12 and so on – and contended that there was no evidence of collusion.

The disbelieving relatives and their lawyers fought on until a new ombudsman, Dr Michael Maguire, reinvestigated the crime. His report in 2016 concluded that there had been collusion between the police and the UVF. The police had sought to protect an informer or informers. It was a vindication, of sorts, for the relatives because an official body had, at last, provided them with the truth.

They were also delighted when the case was taken up by an award-winning US documentary maker, Alex Gibney, who, in company with two Northern Ireland journalists, Trevor Birney and Barry McCaffrey, made a film about the massacre. No Stone Unturned, which was released last year, explores the cover-up in detail, identifies the suspects and produces documentary evidence to prove that collusion had occurred. At a special screening in the National Union of Journalists’ headquarters on Thursday, there were gasps from the audience at some of the revelations.

And here we come to the second act of the farce, although it generates no laughs. In August this year, Birney and McCaffrey were arrested on the grounds that they obtained confidential documentation. They were accused of theft and face being charged under the Official Secrets Act and, possibly, the Data Protection Act. They are now on police bail, which has just been extended until March next year.

In a bizarre twist, they were informed that their arrests were due to a complaint from the police ombudsman’s office. This was swiftly denied by that office, which issued an unequivocal statement to the Irish Times saying: “We did not make a complaint of theft.”

The PSNI, the successor force to the RUC, responded with a claim that a complaint had, indeed, been made. Truth, once more, proves a moving target.

But this is all a giant diversion, of course. Two journalists, who acted in the public interest by shining light on a dark and evil deed, are facing criminal charges while men guilty of a multiple murder walk free, just as they have done for 24 years.

While we defend the messengers, as we should because there are clear press freedom implications in not doing so, their message is, once again, overlooked. A police force colluded with murderers to ensure that justice was not done.

So where, you may ask, was the journalistic failure? Firstly, as so often with Northern Ireland matters, most British news organisations averted their gaze from the “Loughinisland massacre” at the time and for many years afterwards. In 2012, the Guardian took up the relatives’ cause, and in 2016, following the ombudsman’s report, I lamented the lack of journalistic interest. For UK newspapers, there has long been a border down the Irish Sea.

There is another sad media aspect to this affair. At its outset, Gibney’s No Stone Unturned was produced in collaboration with the BBC. One of its former investigative reporters, John Ware, appears on the documentary and is clearly in sympathy with its attempt to get at the truth. But the BBC and Gibney fell out over who should exercise control.

Evidently, the BBC wanted to produce a slightly separate version which would accord with its editorial guidelines. This split is a great pity. As Birney told the NUJ audience: “The relatives were devastated by the film not being shown by the UK’s public service broadcaster.”

I agree. This harrowing film, step by step, frame by frame, deserves as wide an audience as possible. Birney and McCaffrey do not want their arrests to take the centre ground. They do not want to be the story. Because they believe it is tragedy, not farce, that should be the predominant message.